With the increasing integration density and operating frequencies of microelectronic devices, manufacturing processes for these devices require the ability to measure dimensions of submicron structures that make up the devices and thickness of the thin films deposited on, around, or under the structures. These measurements are performed during the numerous lithography, etching, and thin-film deposition steps of the manufacturing process. New transistor generations are built of non-planar structures defined during processing of multilayered films, and these generations require metrology measurements beyond just measuring the multilayered films at each process step.
Optical measurements provide fast, accurate, non-destructive, and relatively inexpensive analysis techniques. As sample structure dimensions become smaller than or comparable to the light wavelength, simple imaging such as microscopy is not possible, and the measurements require analysis of the intensity and/or the polarization state of the light scattered off the sample structure. The simplest analysis and greatest sensitivity are achieved when periodic arrays of sample structures are measured.